The present invention relates to an optical waveguide component used as a fiber stub or an optical attenuator stub in an optical communication system and a method of producing the same.
In an optical communication system, a light emitting module for coupling a light beam from a light source to an optical fiber, a light receiving module for detecting an optical signal from the optical fiber, and an optical attenuator for adjusting an optical power propagating through the optical fiber are important devices. Among these devices, the light emitting module or the light receiving module is provided with an optical waveguide component called a fiber stub. The fiber stub is connected to an optical connector. On the other hand, the optical attenuator is provided with an optical waveguide component called an optical attenuator stub. The optical attenuator stub is also coupled to the optical connector.
The optical connector comprises a capillary tube, called a ferrule, having a high dimensional accuracy. An optical waveguide member is inserted into the ferrule and fixed thereto. Thus, the optical waveguide member is accurately positioned. Therefore, the fiber stub or the optical attenuator stub to be coupled to the optical connector is also required to have a dimensional accuracy equivalent to that of the ferrule. As the optical waveguide member, an ordinary or common optical fiber and an optical attenuation fiber are used for the fiber stub and the optical attenuator stub, respectively.
For example, Japanese Unexamined Patent Publication No. 2000-47036 (JP 2000-47036 A) discloses an optical attenuator stub comprising a ferrule as a positioning member and an optical attenuation fiber as an optical waveguide member inserted into the ferrule and fixed to the ferrule by an adhesive. The ferrule of the optical attenuator stub has a bore diameter greater than the diameter of the optical attenuation fiber by about 1 μm so that the optical attenuation fiber is easily inserted.
However, the above-mentioned optical attenuator stub is disadvantageous in the following respect. When the optical attenuation fiber is inserted into the ferrule, a clearance of about 1 μm is left between the optical attenuation fiber and the ferrule. Therefore, the optical attenuation fiber may be eccentric with respect to the ferrule by about 0.5 μm at maximum. In this event, optical axis misalignment is caused when the optical attenuation fiber is coupled to the optical connector. This may result in an increase in connection loss of an optical signal. Furthermore, a light beam propagating outside a core, i.e., a so-called clad mode, may be increased to interfere with a signal beam. The increase in connection loss due to the above-mentioned eccentricity is a serious problem not only in the optical attenuator stub but also in the fiber stub.
When the temperature is elevated, the optical attenuation fiber may be retracted with respect to the ferrule due to the difference in expansion coefficient between the ferrule and the optical attenuation fiber. This also results in an increase in connection loss. If the temperature is further elevated to become higher than the glass transition point of the adhesive, the adhesive may be deformed or deteriorated. In this event, the fiber can not be held at a predetermined position. As a result, the connection loss is increased and, in the worst case, PC (Physical Contact) connection is impossible so that the light beam can not be guided or propagated at all.
Japanese Unexamined Patent Publication No. H09-152524 discloses a method of producing a fiber stub. The method comprises the steps of preliminarily firing a ferrule as a positioning member, inserting an optical fiber as an optical waveguide member into the preliminarily-fired ferrule, and full-firing the ferrule to thermally contract or shrink the ferrule, thereby fixing the optical fiber to the ferrule. According to this method, the optical fiber can be fixed without using the adhesive. In this respect, the production process can be simplified. In addition, since the optical fiber is fixed to the ferrule in tight contact therewith, it is possible to prevent the optical fiber from being eccentric due to presence of clearance.
However, this method requires a large number of careful and delicate operations of inserting the optical fibers into the ferrules, i.e., capillary tubes one by one. In addition, this method requires a complicated process in which the ferrule is preliminarily fired and then full-fired. It is therefore difficult to obtain an inexpensive product. Furthermore, since the contraction ratio of the ferrule at the firing step widely varies, the position of the optical fiber may be misaligned from a center axis of the ferrule. In addition, it is difficult to achieve a high circularity of the outer diameter of the ferrule. It is therefore required to execute a polishing step of polishing an outer periphery of the ferrule with respect to the optical fiber. This results in an increase in cost.